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The operating conditions of Nordic hydropower plants are expected to change in the coming years to work more in conjunction with intermittent power production, causing more frequent hydropeaking events. Hydropeaking has been shown to be detrimental to wildlife in the river reaches downstream of hydropower plants. In this work, we investigate how different possible future hydropeaking scenarios affect the water surface elevation dynamics in a bypass reach in the Ume River in northern Sweden. The river dynamics has been modeled using the open-source solver Delft3D. The numerical model was validated and calibrated with water-surface-elevation measurements. A hysteresis effect on the water surface elevation, varying with the downstream distance from the spillways, was seen in both the simulated and the measured data. Increasing the hydropeaking rate is shown to dampen the variation in water surface elevation and wetted area in the most downstream parts of the reach, which could have positive effects on habitat and bed stability compared to slower rates in that region.

As intermittent power sources such as solar power and wind power gains traction in Scandinavia it is likely that the electricity production will become increasingly dependent on hydro power as a buffer in times of power deficit from intermittent power sources due to weather conditions. Rapid changes in hydro power demand can rapidly change the flow conditions in proximity to the power plant. This paper aims to model the transient behavior and quantify the inherent damping in a dry reach in proximity to the largest hydro power plant in Sweden, with respect to production. A two-dimensional model solving the Navier-Stokes equations with shallow water approximations was set up using the open-source solver Delft3D. The Manning numbers in the reach was calibrated with measured steady state water surface elevation data. The simulation data was then validated with transient water level measurements. The results show that it's possible to calibrate the Manning numbers using steady state water level measurements. The model also shows that it's possible to capture the inherent damping and more transient behavior using Delft3D. The results can be used to better model rivers without the need for resolving the upstream reach. The results can also be used for ecohydraulical applications where the transient behavior is important

Hydropower tunnels are generally subject to a degree of rock falls. Studies explaining this are scarce and the current industrial standards offer little insight. To simulate tunnel conditions, high Reynolds number flow inside a channel with a rectangular cross-section is investigated using particle image velocimetry and pressure measurements. For validation, the flow is modelled using large-eddy simulation (LES) and a Reynolds-averaged Navier-Stokes (RANS) approach with the k − ε turbulence model. One wall of the channel has been replaced with a rough surface captured using laser scanning. The results indicate flow-roughness effects deviating from the standard non-asymmetric channel flow, and hence cannot be properly predicted using spatially averaged relations. These effects manifest as localized bursts of velocity connected to individual roughness elements. The bursts are large enough to affect both temporally and spatially averaged quantities. Both turbulence models show satisfactory agreement for the overall flow behaviour, where LES also provided information for in-depth analysis.

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